This invention relates to electric current generators and, more particularly, to such generators operating by electrochemical oxidation and comprising at least one cell with an anode compartment and a cathode compartment, or several of such compartments. The invention relates also to a novel and highly-effective process utilizing such generators.
The invention concerns, in particular, generators in which the active material of the anode compartment, sometimes called fuel, is a metal referred to as an anode-active metal, this anode-active metal undergoing electrochemical oxidation in the anode compartment with loss of electrons when the generator supplies electric current to a discharge circuit.
The invention relates, more particularly, to generators whose anode compartment contains a liquid electrolyte in which particles of anode-active metal are present, the electrolyte and the particles being in movement. The electrons lost by the anode-active material during the discharge are then collected in the anode compartment by an electrically conductive member, called the anode collector.
By active metal particles of the anode compartment there are understood particles formed, in whole or in part, of anode-active material, for instance particles whose electrochemically inactive center is covered with a covering formed by anode-active material.
Such an anode compartment is electrochemically associated with a cathode compartment comprising a cathode having a cathode-active material which is reduced by electrons corresponding to the negative charges liberated in the anode compartment during the discharge of the generator, the electric charges necessary for the electrochemical reaction in the cathode being delivered by an electrically conductive member called the cathode collector.
In order to produce generators of relatively high electric power, such generators being intended for instance for the traction of electric vehicles, at least two cells are combined with each other.
The feeding, in hydraulic series, of these cells with the electrolyte containing the active particles permits, in particular, a substantial simplification of the circulation devices, these cells being furthermore connected in electrical series so as to increase the electric voltage at the terminals of the generators.
The anode compartment of one cell, called the first cell, is thus connected to the cathode of the following cell, called the second cell, by an electric conductor of low resistance, the electrical connections being effected by the anode and cathode collectors. The one of these two cells which is first traversed by the electrolyte and the particles is called the upstream cell, the other cell being called the downstream cell, in which connection the upstream cell may be either the first cell or the second cell.
Each anode collector comprises an upstream end and a downstream end with reference to the average direction of the flow of the electrolyte and the particles in the anode compartment in which it is contained. When n identical cells are combined in this manner, one aims at obtaining a generator whose voltage V at the terminals is equal to nv, v being the voltage at the terminals of an isolated cell, and whose electrical power W is equal to nw, w being the electric power of each isolated cell.
In conventional practice, this arrangement results in the following drawbacks:
The placing in electric series gives rise to a short-circuit current for each electric unit, referred to as a hybrid generator, formed of the anode collector of the first cell, the cathode of the second cell, and the electrolyte in contact with this anode collector and this cathode. Such a short-circuit current causes a deposition of anode-active metal at one end of the anode collector of the second cell, this end being hydraulically the closest to the anode collector of the first cell. The expression "hydraulically closest end" means that the path along the electrolyte from said end to the anode collector of the first cell is shorter than the path along the electrolyte from the other end of this same anode collector of the second cell to the anode collector of the first cell, the path along the electrolyte being measured in the direction of flow when the first cell is the downstream cell and in the direction opposite the flow when the first cell is the upstream cell.
The end where this deposition of anode-active metal takes place is therefore an upstream end when the first cell is the upstream cell and a downstream end in the opposite case. The deposit of metal which is produced even when the generator is not delivering current increases progressively and leads, on the one hand, to an obstructing of the anode compartments of the generator which makes the circulation of the electrolyte and particles impossible and, on the other hand, to a short-circuit between the anode collectors of two cells arranged one behind the other by the anode-active metal thus deposited. The generator then rapidly becomes unusable.